In recent years, in a disk array system (referred to also as a storage system and the like), due to the trend toward faster processing in electronic components such as an LSI on a circuit board and faster data transfer between LSIs, consumption power and heat generation in electronic components such as an LSI have been increasing. Although consumption power in an LSI is about 10 to 15 W at present, if it increases to, for example, 20 to 30 W from now on, more effective means for cooling the heat (radiation) is required.
As an example of cooling means for the objects to be cooled such as electronic components on a circuit board, there is a structure in which a heat sink (radiator plate) is provided on the upper surface of each electronic component such as the LSI as the object to be cooled on a flat surface of a circuit board and by which the heat thereof is radiated. In this structure, a heat sink having a surface with almost the same size as the upper surface of the LSI as the object to be cooled is attached to the LSI. The heat sink is made of a material with high thermal conductivity (low heat resistance) and it is composed of, for example, an almost plate-shaped portion as a base part and radiator fins to enhance the radiation by air-cooling. For example, the radiator fin is composed in the following manner, that is, a plurality of cylindrical fins are provided vertically to the surface of the base part. However, this structure is not enough to deal with the increase of the heat generation due to the increase of the consumption power of the LSI, and the heat radiation of the heat sink is not sufficient.
For the improvement of the radiation efficiency by the heat sink, it is effective to enlarge a surface area of the radiator fin so as to increase the area coming in contact with the air. As a method for enlarging the surface area of the radiator fin, first, there is a method to enlarge the surface area of the base part of the heat sink so as to increase the installation area of the radiator fin. Second, there is a method to increase the height of the radiator fin itself of the heat sink.
In the case of the first method, since there are various components mounted around the LSI on the board, when the area of the base part of the heat sink attached on the upper surface of the LSI is increased, it is necessary for the heat sink not to contact the components mounted around the LSI, and therefore, it becomes difficult to mount the components around the LSI. As a result, the problem that a mounting efficiency on the board is lowered arises.
Further, in the case of the second method, a space required for the layout of the heat sink is increased, and it becomes necessary to secure a wide interval with the circuit board to be adjacently mounted in order to sufficiently secure the height of the heat sink when mounting the circuit board in a logic box of a disk array system. Consequently, the size of the logic box is increased and resulting in the increase of the size of the disk array system.
On the other hand, when there is the impedance mismatch on a data transfer path in the circuit board, a reflection noise arises. When the reflection noise arises during the high-speed data transfer, a degradation of signal occurs, and therefore, it is necessary to match a characteristic impedance of the wiring area to be a transmission path of the data transfer and an impedance in electronic components such as the LSIs on a transmission/receiver side which perform the data transfer process in order to reduce the reflection noise. Usually, though a circuit is designed so as to allow these impedances to match, the process and the burden are different between one LSI and the other LSI which perform the data transfer process. Therefore, the heat generation thereof also varies, and as a result, a difference in temperature arises on the paths during the data transfer. When a temperature difference arises between the LSI serving as the main component of the process to be the data transfer path and the wiring area to be the transmission path, the impedance is changed due to the temperature difference and the reflection noise tends to arise easily, and thus, the normal and efficient high-speed data transfer becomes difficult. With respect to this problem, since the heat sink is attached to each LSI as the object to be cooled in the above-mentioned example of the cooling means, it is not possible to reduce the temperature difference between each LSI.
As a technique for cooling the electronic components on the circuit board, a mounting structure of a plate-shaped heat pipe is disclosed in Japanese Patent Laid-Open No. 11-101584. According to this technique, the plate-shaped heat pipe is provided in opposition to the board on which a plurality of elements to be cooled are mounted. The plate-shaped heat pipe is provided with the predetermined convex portions depending on the distance with the opposite elements to be cooled and is fixed to the board by an outer frame attached to the outer peripheral portion of the plate-shaped heat pipe. The heat pipe has a working fluid sealed in a cavity portion of the plate-shaped heat pipe, and the heat is discharged by the phase transformation and the moving action of the working fluid.